188 THE LURE OF THE LAND 



to plant growth. If, however, either nitrogen, potash, 

 or phosphoric acid be entirely removed from the en- 

 vironment, it is impossible to produce a matured plant. 

 The great bulk of the material of which plants are 

 composed is not drawn, however, from the soil, but is 

 taken from the air and water. Great as have been the 

 chemical achievements of man, no chemist has yet 

 arisen whose skill can be compared to that of the plant 

 itself. Any chemist who to-day, with all the appliances 

 which science has placed at his disposal, could make 

 by synthesis the various organic compounds of which 

 plants are principally composed would rival the fame 

 of Berzelius, Liebig, Hoffman, Berthelot, Gibbs, or 

 Curie. Thus the soil must be regarded as that part of 

 plant life which furnishes the physical support for the 

 growing plant, supplies it with the mineral foods essen- 

 tial to its growth and maturity, and favors best those 

 conditions which enable the plant cell to elaborate the 

 organic matters of which the matured plant is chiefly 

 composed. 



CLASSIFICATION- OP SOILS. 



"While there is an infinite variety of detail in the 

 character of the soils of the United States as regards 

 physical qualities and chemical composition, they may 

 be classed into three great divisions as regards their 

 origin, and this classification in a measure also classi- 

 fies them as to physical qualities. 



" First are the drift soils of the !Nbrth, occupying the 

 principal portion of the States lying north of the Ohio 

 and east of the Missouri River. It is a theory of geolo- 

 gists that in a previous age of the earth the northern 

 hemisphere had a very much colder climate than now; 

 that ice in the form of glaciers covered all the more 



